1. Field of the Invention
The present invention relates to an ink set for use in ink-jet recording, which is suitable for use in recording of color images and for storage of recorded images, particularly, an ink set for use in high-quality gradation recording, and also relates to an ink-jet recording process and an image recording apparatus using the ink set.
2. Description of the Background Art
An ink-jet recording method is a recording method, in which ink droplets are ejected from a nozzle provided in a recording head by generating pressure owing to thermal energy, vibration by means of a piezoelectric element, or the like, and the ink droplets are fixed to a recording medium to form images, which method is excellent in stillness and can form high-resolution images at high speed without using a special fixing means. Such a recording method is also suitable for use in formation of color images from the viewpoints of structural easiness, running cost, etc., and in recent years in particular, ink-jet recording processes and apparatus for forming color images have been provided for a great number of uses such as output for personal computers, graphic printing, etc.
In the case of a recording process for forming color images among the ink-jet recording processes, it is general to use at least three primary colors of a cyan ink composition, a magenta ink composition and a yellow ink composition, and images are generally formed with 4 colors plus black in addition to these colors. For example, red is artificially represented by applying magenta and yellow to the same point or adjoiningly, and blue and green are respectively represented by magenta and cyan, and cyan and yellow likewise. Further, gradation properties may be imparted to these colors by controlling the amount of ink droplets or the number of times of the application or by using black in combination therewith.
Color images may be recently formed in some cases with 6 colors including additional 2 colors produced by thinning down the concentrations of the cyan ink composition and magenta ink composition in addition to these 4 colors. Such ink compositions used in the formation of color images are required to develop a good intermediate color when combined with a plurality of ink compositions in addition to the fact that they have good coloring ability by themselves. Further, it is proposed to use a plurality of inks, which have the same hue, but differ in density, in an ink-jet recording apparatus for recording medical images or the like of which reproduction property of half tone is required.
Ink compositions of an ink set used in such ink-jet recording processes are required to have such high performances that, for example, physical properties such as viscosity and surface tension are adequate, images high in optical density and bright or clear in color tone are provided, images excellent in fastness properties such as water fastness, abrasion resistance and light fastness are provided, storage stability is excellent, clogging at an orifice is hard to be caused, and further odor, safety and the like are good.
Since aqueous solutions of dyes are generally used as inks in these processes, in some cases, bleeding may have been caused upon overlapping colors, or a phenomenon called feathering may have appeared in directions of fibers of paper at a recorded portion on a recording medium. In order to improve these problems, it is disclosed in U.S. Pat. No. 5,085,698 to use pigment-dispersed inks.